Lmao it's not. I've thought like that in the past, but I came back full circle to this conclusion.
Many of the other fraternity brothers are probably tall, good looking men, and they attract women to the party. The other fraternity brothers set ratios of 7 women for 1 man at their parties. The good looking members are maybe able to sleep with 1 women a night, maybe 2.
That leaves a lot of room for the guy who wormed in to get something. And social preselection is also working in his favor. I'm not saying he's any woman's first choice ofc. Same logic in social circles.